1. Field of the Invention
The invention relates to portable carriers such as mass memory cards or credit card type chip cards. It can be applied notably to microcomputers.
2. Discussion of the Related Art
Detachable mass memory cards have recently appeared as accessories of personal computers or microcomputers, especially for portable computers. They could replace diskettes and other magnetic type mass storage means in the future. They can be used as mass memories with a capacity as great as that of magnetic diskettes (with a size of about 1 million bytes). Their space requirements are no longer great since they have a credit card format with a thickness of 3 to 5 millimeters and access to them is obtained far more swiftly (several thousands of times more swiftly).
They can even be used as random-access memories for programs that can be directly performed by the personal computer. In this case, unlike in the case of magnetic mass memories, they do not have to be loaded into the random-access memory (RAM) of the PC in order to be performed thereafter. The programs that they contain can be performed directly by the personal computer.
Mass memory cards, sometimes also called PC cards, have several memory chips and a connector at the edge of the card (a female 68-pin connector according to the PCMCIA standard by the "Personal Computer Memory Card International Association", 1030B East Duane Avenue, Sunnyvale, Calif.). The card can be plugged into a corresponding connector (the male connector of the computer). The connections are such that the memory can be addressed by the parallel input-output port of the PC, as if the memory were a magnetic mass memory, namely as if it were an extension of the random-access memory of the computer.
These plug-in cards, apart from their memory function, may provide additional functions such as, for example, functions of communication. Other cards, known as smart cards, have a microprocessor capable of performing programs contained in the RAM memory of the card by itself. It is also planned, in these smart cards, that the computer will be capable of the direct loading, into a memory of the card, of the files that can be directly performed by the microprocessor.
The memory space of these edge-connector memory cards is formatted in the same way as the magnetic diskettes, according to the operation system associated with the microcomputer. In one example, where the operating system is the well known DOS (Disc Operating System), the memory space is divided into sectors of segments. And this memory space is addressed like that of a magnetic diskette. For example, access in reading mode to the fifth sector is got by activating the associated DOS read interrupt command, with the sector number and the number of bytes to be read as arguments.
It is also possible to use control registers of a microcomputer to carry out access operations. Reference will be made, if need be, to the document "PCMCIA socket services interface specification" distributed by "Personal Computer Memory Card International Association" already referred to.
A communications protocol between these cards and an applications program of a microcomputer enables the microcomputer to gain access to the PCMCIA memory space and perform high level commands, namely commands for the initialization/configuration of the card and for the reading/writing/erasure of data.
There also exist other types of portable carriers namely chip cards with flush contacts, widely used in large-scale consumer applications such as telephone cards, cards for access to secured premises, banking cards, etc. These cards generally have only one integrated circuit chip (although it is not ruled out that they may have several of them). The contacts are no longer at the edge of the card but on one of the main plane faces of the card. The contacts are few in number, generally between six and eight. These cards are far slimmer than memory cards using the PCMCIA standard. Their thickness is about 1 millimeter, instead of 3 to 5 millimeters. They are designed to be inserted into readers that are specialized according to applications: telephone booths, turnstiles for the access cards, cash dispensers for the bank cards, etc. They have a memory space managed by a microcontroller or an integrated microprocessor.